1. Field of the Invention
This invention relates to a gang punch tool assembly for punching holes in thin sheet material and, more particularly, to an automated tool assembly for punching a plurality of greensheets in succession comprising a gang punch containing a plurality of punches in a fixed pattern and which gang punch is programmable to activate certain punches to form holes in a desired hole pattern in the greensheets using a die corresponding with the gang punch, the greensheets being automatically fed one by one to the gang punch and die, the greensheet punched, and the punched greensheet then removed and another greensheet positioned for punching.
2. Description of Related Art
In the manufacture of multilayer ceramic (MLC) substrates for integrated circuit semiconductor package structures, a plurality of green ceramic sheets (commonly termed greensheets) are formed by doctor blading a slurry containing a resin binder, a particulate ceramic material, solvents and a plasticizer, drying the doctor bladed sheet and cutting it into appropriate size sheets. Through holes, commonly termed vias, are then punched in the greensheets to facilitate forming electrical interconnections through the sheet when metallized. Electrically conductive paste is deposited in the holes and in appropriate patterns on the surface of the greensheets, the sheets stacked and laminated, and the assembly subsequently fired at a sintering temperature.
The formation of the vias in the ceramic material is accomplished in its green state. Prior to being fired, the greensheets are easily deformed and the precision with which the via holes are formed is greatly dependent upon the use of an apparatus which minimizes distortion or disruption to the structural integrity of the greensheet other than forming the via hole. With the size of electrical components constantly being reduced through technical improvement, the positioning of the vias in ceramic greensheets is becoming ever more restrictive. Further, with the increase in the quantity of the electronic circuits that may be positioned and packaged on a small area of the ceramic substrate, a requirement for a larger number of via holes in the greensheet is evident.
Large numbers of holes must be punched into a greensheet with a high degree of precision in order to properly position the holes. At the same time, this punching operation must occur very rapidly in order to produce the large numbers of greensheets that are necessary in the mass production of electronic components.
A significant portion of the costs associated in manufacturing ceramic packages can be attributed to punching vias in greensheets. A number of factors play a major role in accounting for these costs such as: 1) the high cost for punch die sets customized to a specific product; 2) the long lead-time associated with punch die set fabrication precludes early introduction of a new product; 3) non-customized automated punch die sets have very low throughput for a non-grid product; and 4) automated punch/die sets punches step/repeat numerous times to punch a single sheet resulting in low throughput.
One method for punching greensheets is using a gang-punching apparatus. A gang-punch is a punch/die set where all the punches for a particular ceramic greensheet layer are rigidly and permanently mounted in a fixed plate. The gang-punch is used to punch the entire sheet (layer) with a single stroke. A gang-punch has very high throughput and is cost effective for very high volume products.
Unfortunately, the use of a gang-punch apparatus has drawbacks since the fabrication of dedicated gang-punches with fixed patterns of via holes are not practical for products requiring engineering changes (E.C.""s) or multiple patterns because the same apparatus cannot be easily modified to form different via hole patterns in ceramic greensheets having a different via pattern thereby requiring separate gang-punch apparatus for each E.C. or pattern desired. Additionally, the turn-around time for a new gang-punch/die set is lengthy and high via density is unattainable with single punch heads and usually require multiple punch heads with staggered punches to punch tight grids. The cost is also prohibitive for the punches since for a typical pattern (up) that is specified nine (9) times on each greensheet (9-up) and with each pattern having 2000 (or more) vias, such a 9-up layer would require a gang punch apparatus with a total of 18,000 punches. For a multilayer ceramic substrate composed of ten (10) layers, with each layer requiring a separate gang punch apparatus with 18,000 punches, 180,000 punches would be required to populate these apparatus. At a typical cost of $1 per punch, it would cost $180,000 for the punches alone. Current technology limits for single stroke gang-punching is a minimum punch spacing of about 16 mils.
A number of attempts have been made to provide a gang-punch apparatus which will economically and efficiently provide the means to make via openings in greensheets. One type apparatus utilizes an interposer mask which contains hole openings where holes are desired to be punched. In these apparatus, a plurality of punch elements arranged in a grid are positioned over the greensheet which is covered by the interposer mask. When the punch elements contact the interposer mask as the punch heads are moved downwardly, the holes will be punched where the openings occur since the punch element would pass through the openings in the interposer mask and through the ceramic greensheet. In other areas covered by the interposer mask, i.e., where holes are not desired, the interposer mask will cause the punch element to be retracted into the punch head. Such apparatus are shown in IBM Technical Disclosure Bulletins, Vol. 16, No. 12, May 1974; Vol. 19, No. 4, September 1976 and Vol. 26, No. 10A, March 1984. Other punch apparatus are shown in U.S. Pat. Nos. 4,872,381; 4,425,829; 5,024,127; 5,090,284; and 5,233,895. In U.S. Pat. No. 4,872,381, supra, for example, a programmable magnetic repulsion punching apparatus is shown. A progressive gang-punch is shown in IBM Technical Disclosure Bulletin Vol. 15, No. 2, July 1972 wherein a gang-punch is shown utilizing steel balls on the surface of the punch head at locations of punches to be punched which when a roller traverse the top of the punch head only vias are punched where steel balls are located. The disclosures of the above references and patents are hereby incorporated by reference.
Regardless of the gang punch/die apparatus used, it is equally important to process multiple greensheets rapidly, effectively and efficiently using the apparatus. This requires moving and positioning greensheets to be punched in the gang punch/die apparatus, removing the punched greensheet and then moving and positioning another greensheet for punching. This process is repeated and it is important that each greensheet be processed rapidly without any damage to the greensheet and that the greensheet be properly aligned for punching.
Bearing in mind the problems and deficiencies of the prior art, it is therefore an object of the present invention to provide a gang-punch tool assembly for rapidly punching hole patterns sequentially in a plurality of thin sheet materials such as greensheets.
It is a further object of the present invention to provide a method for punching via holes in greensheets which are sequentially processed rapidly through the gang punch tool assembly apparatus of the invention.
It is another object of the present invention to provide greensheets and other thin sheet materials punched using the method and apparatus of the invention.
Other objects and advantages of the present invention will be readily apparent from the following description.
The above and other objects and advantages, which will be apparent to one of skill in the art, are achieved in the present invention which is directed to, in a first aspect, a gang punch tool assembly comprising:
structural means for carrying a gang punch apparatus which gang punch is actuatable to force punch pins in the apparatus through openings in a die mated with the punch apparatus, a die apparatus, a thin worksheet (e.g. greensheet) feeder device and a punched worksheet (e.g. greensheet) removal device;
reciprocating means to move the die apparatus upwards to mate with the punch apparatus and downward to be separated from the punch apparatus;
means to actuate the gang punch apparatus when the die is mated with the gang punch to force the punch pins in the punch apparatus outward from the apparatus to enter corresponding openings in the die mated with the punch apparatus.
In a further aspect of the invention, the gang punch tool assembly comprises a punch apparatus which is secured to a punch press platen movable up and down in the assembly. In the greensheet punching position, the punch press platen is fixedly secured in the assembly. The punch press platen is preferably fixedly secured in the assembly by wedge shaped locking blocks, movable laterally in the assembly to lock the press platen in a fixed position. The greensheet feeder device and greensheet removal device are preferably vacuum devices which pick up a greensheet from a stack of greensheets to be punched and deliver the individual greensheet to the punch position. After punching, the greensheet removal device is moved over the punched greensheet and preferably by vacuum removes the punched greensheet from the die and moves it to an output station. Another greensheet is then picked up and delivered to the punch position.
It is a preferred feature of the invention that a gang punch apparatus be used which has an expandable pressure chamber which when actuated allows the punch pins to move outward from the apparatus into corresponding openings of a mating die apparatus. Such an apparatus is shown in a patent application filed on even date herewith entitled Low-Cost High-Density Gang Punch assigned to the assignee of the present invention, now U.S. Pat. No. 6,223,636. Punch pins for use in the gang punch apparatus are preferably made as described in an application filed on even date herewith entitled Apparatus And Method For Producing Punch Pins With Spherical Head assigned to the assignee of the present invention.
A pressure chamber is used between guide and stripper plates of the gang punch apparatus to enable the plates to be in an extended non-punching position or a contracted punching position. The pressure chamber may be expanded or contracted depending on the gas pressure within the chamber and the force of a die apparatus mated with the gang punch. The gang punch apparatus in the non-punching position will have air or other gas within the chamber under pressure so that the punch pins are disposed within the guide and stripper plates of the gang punch apparatus. When the apparatus is to be used, the air pressure in the chamber is vented or reduced so that a force exerted on the gang punch apparatus by the die will force the lower stripper plate toward the upper guide plate extending the desired punch pins below the lower surface of the stripper plate into the die and the non-punch pins into the through holes of the clearance plate. After the punching operation, air will be forced into the chamber, expanding the chamber and, once again, stripping or retracting the punches out of the die and punched greensheet and positioning all the punch pins within the guide and stripper plates of the gang-punch apparatus.
A method for punching greensheets is also provided comprising:
supplying a stack of greensheets to be punched;
moving a single greensheet into a gang punch tool assembly comprising:
structural means for carrying a punch apparatus which gang punch is actuatable to force punch pins in the apparatus through openings in a die mated with the punch apparatus, a die apparatus, a greensheet feeder device and a punched greensheet removal device;
reciprocating means to move the die apparatus upward to mate with the punch apparatus and downward to separate from the punch apparatus; and
means to actuate the gang punch apparatus when the die is mated with the gang punch to force the punch pins in the punch apparatus outward from the apparatus to enter the corresponding openings in the die mated with the punch apparatus;
moving a greensheet to the top of the die apparatus;
moving the die apparatus upwards to mate with the punch apparatus;
controlling air in the pressure chamber of the punch apparatus to a low value to allow the punch pins in the punch apparatus to pass through corresponding openings in the die thereby punching the greensheet interposed between the gang punch apparatus and die apparatus;
increasing controlled pressure in the pressure chamber of the gang punch apparatus to remove punch pins in the gang punch apparatus from the die apparatus and punched greensheet;
moving the die apparatus to a position separated from the gang punch apparatus;
removing the punched greensheet using the punched greensheet removal device; and
repeating the above steps to punch a plurality of greensheets.
In another aspect of the invention, greensheets and other thin sheet materials which have been punched using the method and apparatus of the invention are provided.